INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE (ENGLISH)
Year:2001 | Volume:12 | Issue:1|Papers Count:13

There have been many investigations on the life assessment of high temperature weldments used in cylindrical pressure vessels, pipes and tubes over the last two decades or so. But to the author's knowledge, currently, there exists no practical, economical and relatively accurate model for creep life assessment of butt-welded joints in cylindrical pressure vessels. This paper describes a semi analytical and economical model for creep life assessment of butt-welded joints. The first stage of the development of the model is described where the model takes into account the material discontinuities at the welded joint only. The development of the model to include other factors such as geometrical stress concentrations, residual stresses, etc will be reported separately. It has been shown that the proposed model can estimate the redistributions of stresses in the weld and HAZ with an error of less than 4%. It has also been shown that the proposed model can conservatively predict the creep life of a butt-welded joint with an error of less than 16%.

The single crystal alloy SRR9 consists of a r matrix which is strengthened by a fine, homogeneous dispersion of primary coherent g’ particles. A number of SRR9 specimens with orientation close to <011>were subjected to tensile test at different temperatures with a constant strain rate of 3.0´10-5 Sec-1. The orientations of the specimens which were defined by two angles of (q’, r’) in the unit triangle of a stereographic projection were carefully found by Laue back reflection technique and were taken parallel to the stress axis. After testing, cross sections of the specimens were examined by light and electron microscope (SEM) and the observed microstructure deformation and the related tensile properties were justified in terms of Schmid factor. It was suggested that over a temperature range of 20° -90°C, [011] orientated specimens of SRR9 deform primarily by slip on the (111) [101] system while at 975°C it seemd that two slip systems were operative during deformation process, one was (111) [101] and the other was {100} <110>. Attempt was made to justify these suggestions.

In this research work, the isothermal reduction of composite pellets of different iron ore and coal mixtures, in the range of 1000-1150°C was studied The effect of iron ore type on the kinetics of the reduction was investigated by using different iron ore, including Gole-e Gohar, Samarco, CVRD, and Kodermukh. Also, different type of coal, including Pabdana, Sang-rood, Shahrood, Bab Niezoo, and Karmozd, and Karmozd, were used to find the effect of this parameter on the reduction kinetics. It was found that the reduction rate increases with increasing temperature, but the iron ore type does not have any significant effect on the reduction rate. On the other hand, the coal type has a very significant effect on the reduction rate at temperatures below 1050°C. But, above this temperature the effect of coal type was negligible. Based on the results of this study, the activation energy for the reduction reaction of composite pellet is in the range of 150-200 KJ mol-1.

The titaniferous magnetite deposits from Madanagere - Morahalli area, analysing 57.1% Fe, 9.3% TiO2 1.11% V2O5, 3.93% Al2O3 and 1.68% SiO2 have been sampled and used to recover vanadium in the form of sodium hexa - vanadate containing 88.53% V2O5, 8.82% Na2O and 2.76% H2O. The experimental procedures involved are low- intensity wet magnetic separation, salt roasting, leaching and precipitation. The overall V2O5 recovery was 85.8%.

The objectives of this paper are to investigate the identification and mechanism of formation of whiskers formed during heat treatment of graphite containing ceramic-matrix composites. At the conditions of processing i.e., 1500°C under argon atmosphere and presence of silicon in the batch composition, formation of SiC whiskers have been shown. The results show that the mechanism of formation of SiC whiskers is VLS and it seems to be promising from hygienic industrial point of view.

In this study the effects of the surface a condition of steel rebar on its cathodic current efficiency was investigated The catholic current efficiencies for steel rebar with different surface conditions were determined from cyclic polarization experiments. The results showed that cathodic faradic current increased with surface irregularity. Surface condition of steel in saturated calcium hydroxide also had an effect on double layer capacitance.

Various samples of single crystal SRR9, with orientation close to <001> were subjected to tensile test at different temperatures with a constant strain rate of 3.0X10-5Sec-1. The orientations of specimens which were carefully stablished by Laue back-reflection technique were taken parallel to the stress axis. These orientations were defined in the terms of two angles (q, r) in the unit triangle of a stereographic projection. The results show that at temperatures up to about 8000C there is significant anisotropy, with orientations closer to <100> being the strongest; however as the temperature increase to above 800°C the anisotropy is reduced because of thermal activation of additional slip systems. After testing, the specimens were examined by light and electron microscopes (SEM) and the nature of the observed deformation was rationalized in terms of Schmid factors.

The work investigates the processing of ceramic core by injection molding process. The core was prepared by suspending a mixture of vitreous silica and zircon powder having a relatively wide particle size distribution (1-63 mm) together with a thermoplastic type of binder. The mixture was injected into a metallic mould at a temperature of 80°C. The binder removal from the injected piece was done by applying a suitable heat treatment cycle. Debindering was followed by sintering samples at various conditions. Based on the property evaluation and microstructural investigationa heat treatment at 1200°C for 3hrs is considered an appropriate sintering condition.

The objective of the present study was to join silicon nitride ceramic (Si3N4) to molybdenum using a brazing technique. A commercially available Ag- Cu-Ti brazing alloy (Cusil-ABA) was used as the filler metal. Using sessile drop method, it was found that the Cusil alloy was able to wet Si3N4 adequately. Joining experiments were performed at 900°C. The results of the study showed that Si3N4 can be brazed to Mo using Cusil-ABA with no sever degradation of the parent materials. The room temperature four-point bend strength of the Si3N4-Mo joints was found to be about 390 MPa.

A computer controlled electrochemical cell for performing corrosion fatigue and stress corrosion cracking (SCC), has been designed and constructed with a self-aligning scanning reference probe to map the potential variations of tensile specimens. The cell included a unique fiber optic circuit which maintained a constant gap between the scanning probe and the specimen surface. This monitoring device has been named as the "CORRMAP”. It has been utilized to monitor potential variations of various specimens in aqueous environments. The CORRMAP is a diagnostic tool and is capble of indicating crack initiation and its propagation. The acquired potential data can be processed as contour maps of anodic and cathodic regions.

2212 BSCCO powder produced by the EDTA (ethylene diamine tetra acetic acid) gel processing route was sintered in air to produce specimens for Tc determination; the same specimens were examined by analytical transmission electron microscopy (TEM) in order to obtain more detailed information about the crystal structure, grain boundary and crystalline faults of the superconducting materials. Transition to a superconducting state at 92°K (onset) was observed in the sintered samples. The presence of crystalline faults at grains and non-superconducting phases at grain boundaries have been proved by TEM studies.

Components made of silicon carbide are very important ceramic products due to their good resistance against thermal shocks. Homemade of such products having silicate bonding usually have various defects in their structures. In this research effects of alumina addition on the components made of silicon carbide with clay bonding have been investigated, in order to see its effects on mechanical and structural properties such as blistering. Addition of up to 15wt% Al2O3 improved thermal shock resistance and increased bending strength from 25 MPa to 32MPa due to Al2O3 transformation to mullite. However, when the amounts of alumina exceed 15wt% mechanical strength as well as resistance to thermal shock reduced due to remaining of Al2O3 in the components after sintering.

The occurrences of huge reserves of garnet deposits have been reported from different parts of Iran, specially, those of Kohe- E- Gabri (SampleNo.1), Zaman Abad (sample No.2) and Sangbast (sample No.3) areas which are naturally very rich (except Sangbast area) in nature. The ore of these deposits cannot be directly used as abrasives, filter aids and many others because of some impurities present.To know the mineralogical composition, type of garnet, shape of the particles, chemical character and the mesh of grind which plays a vital role in finding out suitable flow sheet design, these samples have been subjected to detailed mineralogical and microscopic studies, sieve analysis, liberation studies and chemical analysis. The results obtained show that, the type of garnet in sample No.1 is Anderadite with grade of 75% which most of its particles are edged rather than rounded where as in sample No.2 and 3 the type of garnet is Almandine with grade of 45% and 8% respectively.In sample No.1 quartz, calcite, wollastonite, magnetite and hematite are the main impurities present in order of abundance and liberation studies showed that optimum mesh of grind is 600 microns, while quartz, calcite, wollastonite, and alusite, diopside, muscovite, biotite and feldspar are the impurities present in sample No.2 with no liberation problem. In sample No.3 quartz, muscovite, chlorite, feldspar, tremolite, calcite and diopside are the impurities persent and particles are free from each other, belew 2000 microns.Based on the characterization studies carried out on these three samples it was suggested that the gravity and magnetic methods would be the suitable separation techniques for sample No.1 with overal recovery of 87% and more than 95% grade of garnet, and sample No.2 with overal recovery of 87.61% and 91.23% garnet grade, while no beneficiation technique was suggested for sample No. 3 because of the garnet content which is very lower than the cutoff grade (20%).